1. Field of the Disclosure
The present disclosure relates to polishing pads, polishing apparatuses, and processes for using polishing pads, and, more particularly, to polishing pads that have pad windows, polishing apparatuses that include such polishing pads, and processes for using them.
2. Description of the Related Art
A pad window within a polishing pad can serve as a portion of a path for laser light for measuring a wafer during a polishing process. The pad window can cause problems due to its configuration within a chemical mechanical polishing apparatus. FIG. 1 includes an illustration of a cross-sectional view of a chemical mechanical polishing (“CMP”) apparatus 10 and a wafer 128. The CMP apparatus 10 can include a platen 12 and a conventional polishing pad 14. The platen 12 can include a platen window 16. The CMP apparatus 10 also includes a laser 18 and a detector 110 that can be used for endpoint detection. The conventional polishing pad 14 includes a first layer 112 that has an opening 114 and a substantially planar polishing surface 116. A pad window 122 lies within the opening 114 in the first layer 112. The pad window 122 has a polishing surface 126. The conventional polishing pad 14 can have a second layer 118, lying between the first layer 112 and the platen 12. Since the second layer 118 is substantially opaque to a radiation beam from the laser 18, an opening 120 in the second layer is formed such that there is a path for the radiation beam to pass from the laser 18 to the wafer surface and back to the detector 110.
The path is intermittently formed such that a measurement, using the laser 18 and the detector 110, can be taken when the pad window 122 lies between the platen 12 and the wafer 128. However, changes in temperature during polishing can distort the polishing surface 126 of the pad window 122. Distortion can cause problems with a polishing process. Examples of such problems can be a false or absent reading of endpoint detection, part or all of the pad window 122 becoming separated from the rest of the conventional polishing pad 14, excessive wear or a breach of the pad window 122, or any combination thereof. The interaction of distorted polishing surface 126 and a wafer 128 during a polishing process can also damage the wafer 128, the CMP apparatus 10, or any combination thereof.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention. The use of the same reference symbols in different drawings indicates similar or identical items.